1. Field of the Invention
The present invention relates to an organic light emitting display and more particularly to an organic light emitting display and a degradation compensation method thereof capable of compensating for degradation of an organic light emitting diode.
2. Discussion of the Related Art
An organic light emitting display, which has been considered as the next generation display, includes a self-emitting element capable of emitting light by itself. Thus, the organic light emitting display has advantages of fast response time, high light emitting efficiency, high luminance, wide viewing angle, etc.
The organic light emitting display includes an organic light emitting diode (hereinafter, abbreviated to “OLED”) serving as the self-emitting element. The OLED includes an anode electrode, a cathode electrode, and an organic compound layer formed between the anode electrode and the cathode electrode. The organic compound layer includes a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer. When a driving voltage is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer and electrons passing through the electron transport layer move to the light emitting layer and form excitons. As a result, the light emitting layer generates visible light.
In the organic light emitting display, pixels each include an OLED are arranged in a matrix form, and brightness of the pixels is controlled based on a gray level of video data. The organic light emitting display is mainly classified as a passive matrix organic light emitting display or an active matrix organic light emitting display using thin film transistors (TFTs) as a switching element. The active matrix organic light emitting display selectively turns on the TFTs serving as an active element to select the pixel and holds the light emission of the pixels using a hold voltage of a storage capacitor.
There are several factors to reduce the luminance uniformity between the pixels in the organic light emitting display. For example, a deviation between electrical characteristics of driving TFTs of the pixels, a deviation between cell driving voltages of the pixels, a degradation deviation between the OLEDs of the pixels, etc. have been known as the factors. Among these factors, the degradation deviation between the OLEDs leads to an image sticking phenomenon, thereby reducing image quality of the organic light emitting display.
The OLED is degraded by use over a period of time, and thus reduces a display luminance of the organic light emitting display. A degradation degree of the OLED is affected by brightness of an input image. A degradation degree of the OLED mainly displaying a bright image is greater than a degradation degree of the OLED mainly displaying a dark image. Degradation degrees of elements on an organic light emitting display panel are partially different from one another. When the degradation is generated in the organic light emitting display as described above, a related art organic light emitting display compensates for a luminance depending on the degradation degree and uniformly adjusts a display luminance of one screen. The related art increases an amount of current flowing in the OLED in proportion to the degradation degree, thereby compensating for the luminance. Therefore, the related art imposes a strain on a degraded area and accelerates the degradation. In the related art, because an amount of current applied to the element, in which the degradation is accelerated, has to increase, the degradation of the organic light emitting display is accelerated. Hence, life span of the organic light emitting display is further reduced.